Development of a semicircular bend (SCB) test method for performance testing of Nebraska asphalt mixtures.

PDFTech ReportSPR-P1(15) MPMC0726-1121-4023-001Asphalt concrete pavementsAsphalt mixturesBend testsFracture mechanicsAnalysis of varianceTest proceduresStatistical analysisNebraskaMid-America Transportation CenterNsengiyumva, GabrielKim, Yong-RakYou, TaesunUniversity of Nebraska--Lincoln. Dept. of Civil EngineeringNebraska. Dept. of RoadsUnited States. Federal Highway AdministrationUnited States. Federal Transit AdministrationUnited States. Dept. of Transportation. Research and Innovative Technology AdministrationUS Transportation CollectionGranted that most distresses in asphalt (flexible) concrete (AC) pavements are directly related to fracture, it becomes clearthat identifying and characterizing fracture properties of AC mixtures is a critical step towards a better pavement design.This report examines the testing variables of a reliable and practical semicircular bending (SCB) test for evaluating thefracture characteristics of asphalt concrete mixtures at intermediate service temperature conditions. The first part of thisreport investigates the repeatability of the SCB fracture test method by integrating a statistical-experimental approach toidentify testing variables of the SCB test that result in repeatable test results. Toward this end, five testing variables (thenumber of testing specimens, specimen thickness, notch length, loading rate, and testing temperature) of the SCB test wereinvestigated due to their significant effects on mixture fracture characteristics. After statistical analysis of 18 specimenstested with a typical testing variables, approximately, five to six specimens/replicates were found to be a reasonable samplesize that could properly represent asphalt concrete fracture behavior using the SCB test method. The coefficient of variation(COV) of the mixture fracture energy was used to evaluate the effect of each variable on the repeatability of test results. Arange of 1 mm/min. to 5 mm/min. for the loading rate, a notch length from 5 mm to 25 mm, and a specimen thickness of40 mm to 60 mm and a testing temperature of 15-40\uc2\ub0C showed a good repeatability of fracture energy with small COVs(\ue2\u2030\ua415 %). The second part of this work is to investigate the sensitivity of the SCB test using the previously determinedtesting variables. Fourteen different asphalt concrete (AC) mixtures collected from 12 field construction projects inNebraska were used in this task. The ANOVA test showed statistically significant differences between mixtures at a 95%confidence level. Tukey\ue2\u20ac\u2122s HSD multiple-comparison analysis found similarities within mixtures of same types anddifferences between mixture types. In addition, the fracture energy of bituminous mixtures increased with increasing amountof virgin asphalt content in mixture. Overall, the SCB test method developed herein proved to be repeatable and sensitiveto changes in mixtures, and thus a promising tool for evaluating the fatigue fracture resistance of AC mixtures